Well, it's subjective, of course. What was novel to me was the listening-for-sounds system which really made the stealth parts far more immersive and enabled them to play with dark and cramped stealth levels without it becoming impossible to beat.

Also I felt it was the pinnacle of Naughty Dog storytelling, driven by the lessons they had learned in the excellent Uncharted series. The fact they were able to create a game in which nearly the entire time is spent side-by-side with an AI-driven character you start to really care about was quite an accomplishment.

One more thing that sticks out for me is that I'd say Last of Us has the most gripping prologue / first ten minutes I have ever seen in a video game, and that that narrative is held quite taut throughout the game.

The game has an average rating of 95 on Metacritic, so I realize this is the mainstream take on it, but I still think the hype is justified in this case.